1. Spin Delocalization in Electron-Rich Iron(III) Piano-Stool -Acetylides. An Experimental (NMR) and Theoretical (DFT) Investigation.
- Author
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Frédéric Paul, Grégory da Costa, Arnaud Bondon, Nicolas Gauthier, Sourisak Sinbandhit, Loic Toupet, Karine Costuas, Jean-François Halet, and Claude Lapinte
- Subjects
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PROTONS , *RELAXATION phenomena , *NUCLEAR magnetic resonance , *BARYONS , *PHYSICAL & theoretical chemistry - Abstract
Several paramagnetic electron-rich Fe(III) mononuclear arylacetylide complexes of formula (2-dppe)(5-C5Me5)Fe(CC−Ar)in which Ar represents a functional aryl group were studied by means of multinuclear NMR. All signals detected for the various nuclei were assigned. Hyperfine coupling constants for selected nuclei of the arylacetylide ligand were derived from 1H or 19F NMR contact shifts. These NMR data are diagnostic of a metal-centered unpaired electron partly residing in a molecular orbital on the arylacetylide ligand, in line with DFT computations. We show here that the 1H NMR paramagnetic shifts of the ortho (H1) and meta (H2) arylacetylide protons convey decisive information on the charge distribution in the aryl ring. Estimates of the relaxation rates of the unpaired electron were also derived from half-widths of the 1H NMR signals. Finally, line-broadening studies of Fe(II)/Fe(III) mixtures allowed extracting the self-exchange rates for several redox couples among these complexes. The self-exchange rates appear slightly substituent dependent and are apparently larger for compounds with electron-withdrawing substituents on the aryl ring. Reorganization energies of ca. 4000 cm-1could be derived for these outer-sphere electron-transfer processes. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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